The state of flocculation of a papermaking slurry is very important to the runnability of that slurry on a paper machine. The state of flocculation is affected by both mechanical factors and chemical factors. The mechanical factors are usually optimized as best they can be and then chemical additives are utilized to control the state of flocculation. The state of flocculation influences the machine drainage, response to vacuum, retention, pressing and drying conditions. These factors in turn influence the strength and optical properties of the sheet. Two major non-mechanical factors affecting additive performance are the state of the electrokenetic charge in the system and the quantity of fine solids present. The materials which affect these factors have often been referred to as "anionic trash". Zeta potential has been used to monitor the state of charge present in the system. This measurement, although conceptually correct, is difficult to obtain on an online basis in a paper mill. Sensors have been developed for online usage but have not been widely applied. The Zeta potential measurement only gives magnitude of charge and not the total quantity of charge in the system. To speak to this need the colloid titration technique has been developed and instrumented. The technique is proposed as a means to control additive addition rates in the papermaking system. A current study has shown this technique to have limited value. A better technique is to monitor the cationic demand of the papermaking slurry. This approach is used in an off-line mode of operation by many chemical supplier companies. This approach conceptually is correct but suffers the same problems of measurement difficulties as the Zeta potential since it uses Zeta potential to determine its end point and is relatively cumbersome and time-consuming to employ in an effective on-line mode.
Stricter governmental requirements for controlling the contaminants from papermaking effluents in additon to attrative cost saving potential has led the paper industry toward increasing degrees of closure of the papermaking process and white water re-use via recycling. However, such a practice leads to an increase in the build-up of organic and inorganic contaminants and fines in the recycle white water.
The anionic organic moieties in the papermaking slurry complete with the filler and fiber constituents of the papermaking stock for adsorption of the costly cationic chemicals used to influence the retention, drainage and other important factors in the papermaking process.
Under present practice, the use of costly chemical additives has proceeded on a trial and error basis to attempt to improve retention and drainage in papermaking processes. This practice has proven only minimally satisfactory because a reliable monitoring and control strategy has not been devised which offers a convenient and reliable indication of the parameters which influence cationic demand of the papermaking slurry and hence the control of the addition rate of cationic materials used to neutralize anionic contaminants for more effective use of cationic and anionic additives.
Since system upsets can easily occur in paper mill operations, lack of a relatively convenient and sufficiently reliable control parameter often leads to errors in the necessary chemical addition rate and failure to achieve the desired quality of product or a significant increase in costs or both. This is true irrespective of the degree of recycling of the white water, although it becomes more significant as the system is closed and the degree of recycling increases above 80% of so.
The current procedure of utilizing Zeta potential measurements, colloidal titration techniques or direct off-line cationic demand monitoring has not provided a satisfactory solution to the problem of achieving satisfactory control techniques necessary to maximize the desirable economic and evironmental results in papermaking processes.